The present invention relates to a device for inhalation of a pharmaceutically active substance comprising means for generating a negative pressure or vacuum and to a method by which any suitable substance may be prepared in a dispersed state.
Inhalable pharmaceutically active substances are generally used for the treatment of diseases in the bronchial and pulmonary area, such as asthma and chronic bronchitis. Various types of inhalation devices or apparatus are used for this purpose.
One type of inhalation device is the breath-actuated inhaler, particularly but not necessarily a dry powder inhaler, containing multiple doses of a medicament containing an active substance. The inhaler has a manoeuvring means comprising a manoeuvring element for loading one dose of the medicament to a dosing unit and providing said dose in a position for inhalation. An inhaler of the prescribed type is described in EP-A-0 069 715 and EP-A-0 237 507.
The function of this type of known device depends on the creation of an airflow through the inhalation device resulting from inhalation by the patient. The airflow causes the active substance to be moved from a release position in a dosing unit into the airflow in which it is dispersed. A break down of aggregated particles must also be achieved during inhalation, because aggregates always occur in powders having fine particles, especially finely divided powders of the type generally used for inhalation. A particularly advantageous inhaler of the above mentioned type is the dry-powder, breath-actuated, multi dose inhaler TURBUHALER.RTM., generally described in the above mentioned EP-patents.
Some patients such as small children and elderly people with diseases in the bronchial area are not able to use breath-actuated inhalers as it can be hard or even impossible for these patients to achieve the necessary inhalation flow. Airflow needed is about 30-60 l/min and many patients such as small children and elderly people are not capable of producing the necessary inhalation flow. These patients have to use inhalers with pressurised gas, i.e. freon CFC). Such inhalers suffer from many known disadvantages, such as unwanted side effects both for the environment and the patients.
In order to facilitate the inhalation of pharmaceutically active substances which are administered by the use of pressurised metered dose inhalers, so called pMDI:s, it is known to provide dispersion chambers having a considerable volume, e.g. up to 2000 ml, into which the substance, with the pressurised gas, is dispersed. These devices are generally called "spacers" and a typical spacer is known from GB 1 565 029.
Inhalation devices including dispersion chambers have also been developed for breath-actuated, dry-powder inhalers of the above mentioned type. Such an inhalation device is described in EP-A-0 548 152. This device comprises a reservoir for the active substance (this can be part of a dry powder inhaler arranged inside the inhalation device) and a dispersion chamber. The dispersion chamber has a movable wall part which varies the volume of the dispersion chamber between minimum and maximum volumes so as to draw active substance into the dispersion chamber from the dry powder inhaler. The movement of the movable part is achieved by the movement of a piston which when lowered creates a negative pressure within the dispersion chamber. The active substance is thereby drawn out into the chamber. A patient may then inhale the dispersed substance in the dispersion chamber through a face mask or mouth piece. This device is complicated and difficult to use. Furthermore, contact with powder and the design of several mechanical parts make the function of the device less reliable.